[GRASS-user] Custom Projection Problems

[Casey Vandenberg]

I am trying to create a new project using a custom proj4 string. The 
parameters I specify are '+proj=utm +zone=6 +ellps=clark66 
+towgs84=-5,135,172'. After creating the project however, and verifying 
the projection settings using *g.proj -j -f -p* I get the following info:

-PROJ_INFO-------------------------------------------------
name       : Universal Transverse Mercator
proj       : utm
ellps      : wgs84
zone       : 6
towgs84    : -5,135,172,0,0,0,0
no_defs    : defined
-PROJ_UNITS------------------------------------------------
unit       : Meter
units      : Meters
meters     : 1
+proj=utm +no_defs +zone=6 +a=6378137 +rf=298.257223563 
+towgs84=-5,135,172,0,0,0,0 +to_meter=1

Why is it not maintaining the Clarke 1866 Elliposid?



Alternatively, if I specify a proj 4 string as follows: '+proj=utm 
+zone=6 +datum=nad27 +towgs84=-5,135,172' and verify the created 
projection using g.proj, I get the following output:

-PROJ_INFO-------------------------------------------------
name       : Universal Transverse Mercator
proj       : utm
datum      : nad27
ellps      : clark66
zone       : 6
no_defs    : defined
-PROJ_UNITS------------------------------------------------
unit       : meter
units      : meters
meters     : 1
+proj=utm +no_defs +zone=6 +a=6378206.4 +rf=294.9786982 
+towgs84=-22.000,157.000,176.000 +to_meter=1

Here it is maintaining the correct ellipsoid, but it does not maintain 
the towgs84 datum transformation parameters.



Is this a bug or is my interpretation of creating custom projections 
completely wrong?

Thanks,

Casey

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